1. Field of the Invention
The present invention relates to a piezoelectric element, a method of manufacturing the same, and an ink jet head.
2. Description of the Related Art
An ink jet recording apparatus discharges liquid droplets (ink) from fine nozzles and form an image composed of a group of dots formed by the liquid droplets on a recording medium such as a sheet. The performance of this type of ink jet recording apparatus greatly depends on the performance of an ink jet head.
FIG. 6 shows an example of the structure of a general ink jet head. An ink jet head 100 includes a substrate 130 in which a pressure chamber 120 that stores a liquid (ink) and applies pressure, a flow path 122, a discharge port 124, and a supply hole 126 through which a liquid is supplied from a tank (not shown) filled up with a discharge liquid to the pressure chamber 120 are formed. A piezoelectric element that applies pressure to the liquid stored in the pressure chamber 120 is provided on the substrate 130 with an insulating film 104 interposed therebetween. The piezoelectric element includes a lower electrode 106, a piezoelectric layer 108, an upper electrode 110, a protective film (barrier film) 112, and a wiring line 114 connected to the upper electrode 110.
For example, in an ink jet head or a FeRAM using the piezoelectric element, the piezoelectric layer is one of the important elements.
For example, Japanese Patent Application Laid-Open (JP-A) No. 10-34922 discloses a method in which, when a piezoelectric ink jet head is manufactured, a groove is formed in a portion of a piezoelectric film corresponding to a gap between pressure chambers by, for example, dicing, thereby forming plural piezoelectric layers forming piezoelectric elements.
Japanese Patent Application Laid-Open (JP-A) No. 10-226071 discloses an ink jet head in which an insulating layer is formed so as to cover the upper surface of an upper electrode and the side surface of a piezoelectric layer in order to prevent stress concentration and the deterioration of the piezoelectric layer due to a leakage current between the upper and lower electrodes or moisture absorption.
Japanese Patent Application Laid-Open (JP-A) Nos. 11-78002, 2000-85124, and 2008-235569 disclose ink jet heads in which a piezoelectric layer having a trapezoidal shape in a cross-sectional view in a thickness direction is formed to prevent damage due to stress concentration, improve mechanical strength, and prevent a leakage current. For example, Japanese Patent Application Laid-Open (JP-A) No. 2008-235569 discloses a structure in which the side surface of a ferroelectric layer is inclined at an angle of 45° or more in order to ensure sufficient displacement and the side surface is inclined at an angle of 75° or less in order to adhere a large number of plasma particles to the side surface of the ferroelectric layer crystal to restore a crystal state.